The invention relates to an apparatus for the measurement of the transit time of electromagnetic waves, in particular light waves.
In a known apparatus of this kind (German Patent 34 29 062) the individual pulses transmitted by the pulse generator are formed into a roof-like pulse with a clear peak and a differentiation of the pulse signal takes place in the pulse reception time detection circuit, whereupon a zero passage detection of the differentiated signal subsequently takes place. Through the differentiation of the pulse ramps there arises a positive and negative region in which noise signals of a signal are permitted and remain without consequences for signal processing. This region is however dependent on the signal and requires analog signal processing in the amplifier. Simple limiting amplifiers cannot be used here because a limitation of the signal would lead to the flank information being destroyed. As the integral of the permissible noise range is required, whereby an energetic coupling with the length of the measurement region arises, the energy of the transmitted pulse is only inadequately exploited.